Low melting vanadate glasses

ABSTRACT

Glasses are disclosed that melt at low temperatures in the range of 500*-900*C. and that are composed essentially, by weight, of 25-85 percent vanadium oxide, 5-60 percent lead and/or cesium oxide, and 5-45 percent arsenic oxide. The glasses may be adapted either for encapsulating and sealing electrical elements, or for the fabrication of semiconducting elements.

United States Patent 11 1 Malmendier et a1.

14 1 May 27, 1975 I 1 LOW MELTING VANADATE GLASSES [75] Inventors: Joseph W. Malmendier; Joseph E.

Sojka, both of Corning, NY.

173] Assignee: Corning Glass Works, Corning,

221 Filed: May 9,1974 21 App1.No.:468,499

Related US. Application Data [63] Continuation-impart of Serv No. 247.118 April 24.

1972, Pat No. 1837366.

1,015,580 9/1957 Germany 106/47 R 1,015,993 9/1957 Germany l 106/47 R 1,496,562 8/1969 Germany 106/47 R OTHER PUBLICATIONS Stanworth et a1. Chemical Abstracts," Vol. 54, item 178311. Baltz, R, Chemical Abstracts, Vol. 67, item 160772.

Rawson, Inorganic Glass-Forming Systems, (1967). Acedemic Press London & NYC pp 191-193.

Primary ExaminerWinston A. Douglas Assistant Examiner-Mark Bell [52] U.S. C1 106/47 R Attorney Agem, or Firm climon S James Jr; [51] Int. (,1. C03c 3/12 Clarence R Patty Jr [58] Field 01' Search 106/47 R, 47 Q, 49;

[57] ABSTRACT [56] Reerences cued Glasses are disclosed that melt at low temperatures in UNITED STATES PATENTS the range of 500-900C. and that are composed es- 6/1937 Rosenberg 106/49 sentially, by weight, of 25-85 percent vanadium oxide, 1061198 Babcock 106/47 R 5-60 percent lead and/or cesium oxide, and 5-45 per- 3370966 2/1368 i l 06/49 cent arsenic oxide. The glasses may be adapted either "m R for encapsi lating and sealing electrical elements, or

for the fabrication of semiconducting elements.

FOREIGN PATENTS OR APPLICATIONS 1.015.579 9/1957 Germany 106/47 R 6 Clam, 3 Drawmg Flames '1 v 0 \L L V i/ C5 0 20 4O 6O 80 PhD MOLE 1 LOW MELTING VANADATE GLASSES This application is a continuation-in-part of copending application Ser. No. 247,118, filed Apr. 24, 1972 now US. Pat. No. 3,837,866.

This invention relates to vanadate glasses that melt at relatively low temperatures. It is particularly concerned with an additive that stabilizes; that is, inhibits uncontrolled devitrification in, lead and cesium vanadate glasses without substantially increasing the glass softening and melting temperatures. The resulting glasses may be either oxygen rich, or oxygen poor, depending on the batch ingredients selected and the manner of melting. Oxygen-rich glasses may be employed as sealing glasses in the joining of ceramic and/or metal parts, and may also be used in the encapsulation of electrical and electronic components. Oxygen-poor glasses have markedly lower resistivity values which enable them to be used in the fabrication of semiconducting elements.

There is a considerable body of knowledge extant in the glass and electrical arts regarding the use of glass, either in the glassy or in the devitrified form, to seal or join ceramic and/or metal parts. For example, US. Pat. No. 2,642,633, issued June 23, 1953 to R. H. Dalton, describes lead borosilicate glasses for producing glass seals between glass and/or metal parts, while US. Pat. No. 2,889,952, issued June 9, [959 to S. A. Claypoole, describes lead zinc borate sealing glasses that thermally devitrify during or after sealing. More recently, these solder or soft sealing glasses have found extended application as encapsulations for electronic components such as integrated circuits. Glasses used for this purpose, and the process of applying such glasses, are described in detail by D. W. A. Forbes in an article entitled, Solder Glass Seals in Semi-conductor Packaging, in Glass Technology, Vol. 8 (2), pp. 32-42 (1967).

Commercial sealing glasses of the type described by Dalton and Claypoole, as well as simple lead borate glasses, are widely used, but this use is limited by their application temperatures. While such glasses provide satisfactory seals, the temperatures required to insure hermetic sealing or encapsulation are prohibitive for certain purposes. It is of course well known that many electronic components are quite sensitive to even moderately elevated temperatures. Chalcogenide glasses have been proposed as a solution to the problem of lower temperature glass application. However, these glasses have generally proven difficult to handle and apply to a surface.

A basic purpose of the present invention is to meet the apparent need in the electrical art for an improved low melting sealing glass. A more specific purpose is to provide soft sealing glasses that have utility at lower temperatures than the borate type glasses presently in commercial use. A particular purpose is to provide such a sealing glass wherein the crystallization temperature of the glass is sufficiently removed from the glass softening point that the glass can be maintained in the glassy state without uncontrolled crystallization occurring during a sealing process.

It has previously been recognized that soft or low melting glasses can be produced by melting together the oxides of lead and vanadium over a portion of their binary composition range that includes the eutectic at lPbO lV O Rawson reports, on page I92 of his text Inorganic Glass Forming Systems" I967) Academic Press, that Denton et al. prepared binary vanadate glasses of different types. These included a series of lead vanadate glasses within the composition limits of 54-38 percent by weight lead oxide and 46-62 percent by weight vanadium oxide upon which a study of the electrical properties was conducted. MacKenzie also reports, on pages l3 1-] 32 of his text Modern Aspects of the Vitreous State," Vol. III (1964) Butterworths, that a Fe O -Pb()-V O glass has been made and that its electrical properties have been studied. However, writers in this field indicate that most of the studies concerning vanadate glasses have been made on V O -,-P O type glasses.

The present invention is based on the addition of an oxide of arsenic to lead and cesium vanadate melts. These melts are in the vicinity of the PbO:\/ O binary eutectic which crystallizes at about 480C. and the Cs O-V O eutectic existing, in terms of mole percent, at 40% C5 0 and 60% V 0 which has a crystallization temperature of 380C. However, neither eutectic melt could be cooled to a glass and measurements made thereon utilizing normal glassmaking procedures. The arsenic oxide addition to either a lead or cesium vanadate composition provides several salutary effects. First, it tends to increase the difference between the glass softening point temperature and the temperature at which crystallization will occur when the glass is reheated during a forming operation. This stabilizes the glass and provides a wider temperature area or zone within which a glass can be formed and subsequently used without danger of uncontrolled crystallization occurring. Further, it provides a broader composition area within which glasses can be successfully produced. Finally, the glasses, being stable, are suitable for sealing glass use.

The present invention is a low melting vanadate glass having a composition, as calculated in weight percent from the glass batch on the oxide basis in terms of C5 0, PbO, As O and V 0 consisting essentially of 25-85 percent by weight V 0 5-60 percent by weight C5 0 and/or PbO, 5-45% A5 0 and 0-l5 percent of B203, Sb203, T1203, T602, 8602, Ag O, Tiog, 8 1203, Fe O HgO, Ba(), and SnO When both Cs O and PbO are present, the glass consists essentially of 5-60 percent Cs O PbO, wherein both Cs O and Pbo are present in amounts greater than incidental impurity levels, 5-45% As O 25-85% V 0 and O-l5 percent of optionals. in the absence of cesium, the glass preferably consists essentially of 35-60 percent V 0 25-60 percent PbO, 5-30 percent AS203, and 0-15 percent of optional ingredients. In the absence of lead, the glass consists essentially of 35-80 percent V 0 5-55 percent C5 0, 5-25 percent AS203, and O-l 5 percent of optionals.

A small addition of an oxide of arsenic tends to stabilize a lead or cesium vanadate melt by enlarging the difference between the crystallization and softening points. As the arsenic oxide content is increased, however, the coefficient of thermal expansion increases and the arsenic oxide content should not exceed 45% in any event.

The glass softening point as well as coefficient of thermal expansion decreases with increasing content of vanadium oxide. However, it becomes increasingly difficult to maintain a stable valence or oxide level, and hence a stable melt, as the V 0 content increases.

An increase in either cesium or lead content tends to increase the coefficient of thermal expansion. Also,

glasses with a high cesium content tend to be hygroscopic. Accordingly, the contents of these constituents should be limited as indicated. In general, a lead oxide glass is preferred where coefficient of thermal expansion is a factor since the lead glasses tend to have lower expansion coefficients.

The various optional oxides have little effect on the present glasses provided their content is limited as indicated. The halides, when used in substantial amount, tend to soften the glass. but also substantially increase the coefficient of expansion. Other common glassmaking oxides, such as SiO P and A1 0 should generally be avoided, except in trace amounts. Likewise, a characteristic of the present glasses is essential freedom from the more common and relatively mobile alkali metals, lithium, sodium, and potassium.

The invention is further described with reference to the accompanying drawing wherein,

FIG. I is a ternary diagram of the PboAs O -V O composition system, and

FIGS. 2 and 3 are enlarged partial ternary diagrams for batch systems for production of glasses within a portion of FIG. 1.

FIG. 1 shows in solid lines that portion of the lead oxide-arsenic oxide-vanadium oxide system that has been found particularly useful for present purposes. FIGS. 2 and 3 represent alternative batch systems for producing glasses within that portion of FIG. 1 shown in dotted lines. FIG. 2 is based on the PbO-As O -V O batch system, while FIG. 3 shows a corresponding portion of the PbO -As O -V O batch system. Each point enclosed in a circle on the graphical illustrations illustrates a glass batch of corresponding oxide composition. The data adjacent these points indicate l the softening point of the resulting glass in degrees C. and (2) the coefficient of thermal expansion in units/degree C. X

Property measurements made on such comparative glasses demonstrate that, in general, the coefficient of thermal expansion increases and the softening point of the glass decreases as the oxygen content of the glass increases. Thus, a higher oxygen content glass may be achieved by employing PbO (rather than PbO) and/or As O (rather than A5 0 in the glass batch composition. Likewise, a higher oxygen content may be insured in a glass by employing oxidizing melting conditions such as through the use of nitrates as batch materials and/or the use of an oxygen enriched atmosphere over the crucible during melting. The latter is particularly important where longer melting times are employed because there is a marked tendency for vanadium oxide to lose oxygen and change from the pentavalent (V 0 state to the trivalent (V 0 state.

Conversely, the use of lower oxides (PbO or A5 0 in the glass batch and/or the use of reducing conditions during melting leads to a glass having a higher softening point and a lower coefficient of thermal expansion. Such conditions, however, also decrease the electrical resistivity of a glass. Therefore, physical properties in the present glasses may be selectively varied and controlled by controlling the level of oxygen supplied by the batch materials, the melting atmosphere, or both oxygen sources, during the melting process.

In the present glasses, the various cations may be introduced into the glass in different valence or oxidation states. e.g. PbO or PbO as indicated above. Likewise, they may be introduced as the nitrite, nitrate, or other compound form, depending on the oxygen level desired, Finally, they may be introduced in part at least as the fluoride or chloride. In substantial amounts, a halide softens the glass, but also raises the coefficient of thermal expansion. As a matter of convenient reference, however, glass compositions are calculated in oxide form in terms of the oxides PbO, A5 0 and V 0 regardless of the chemical nature or degree of anion content.

The present glasses may be treated in accordance with standard or conventional practices for sealing applications. Thus, they may be reduced to a fine state of subdivision and mixed with a suitable vehicle or carrier. If desired, preformed sealing buttons or gaskets may be formed. For encapsulation, the component may be coated by brushing or spraying. Alternatively, it may be immersed in a slurry of the glass. Finally, where the co efficient of expansion is too high, the glass may be mixed with an inert additive such as zircon (ZrSiO,) in accordance with the practice described in U.S. Pat. No. 3,258,350 granted June 28, 1966 to F. W. Martin and F. Zimar.

The invention is further described with reference to specific exemplary compositions, several of which are set forth in Tables I, II, and III in mole percent and in percent by weight as calculated from the glass batch. Table I sets forth compositions for lead vanadate glasses modified by addition of an arsenic oxide; Table II does the same for cesium vanadate glasses; Table III sets forth illustrative compositions of lead-cesiumarsenic-vanadate type glasses. Table I also gives batch compositions in mole percent to further illustrate the manner in which properties vary between oxygen rich and oxygen poor glasses. In addition to composition data, measurements in C. are given for the glass annealing point (TA softening point (T crystallization point (Tr), melting point (TM); HlSO- average efficient of thermal expansion over the range 25- l50C. (Exp. X 10 /C.)

TABLE I Batch in Mole 7( V 0 47.5 47.5 60.0 60.0 A5 0 5.0 10.0 AS 0 5.0 l0.0 PbO 47.5 30.0 30.0

PbO 47.5

Glass in Molc V 0 47.5 47.5 60.0 600 A5 0, 5.0 5.0 10.0 10.0 PbO 47.5 47.5 30.0 30.0

Glass in Weight "1' V 0 42.7 42.7 55.7 55.7 Asp, 4.9 4.9 l0.l l0.l PbO 52.4 52.4 34.2 34.2

Properties T, 265 245 267 255 Ty 328 280 308 290 T 365 295 323 3l0 T 468 440 507 530 Exp. X IO F'C l l8 I404 l0l l l4.3

Batch in Molc if V 0 600 50.0 50,0 50.0 As O 25.0 A20 I00 25.0 25.0 PbO 25.0 PbO; 30.0 25.0 25.0

Glass in Mole it v 0, 60.0 50.0 50.0 50.0 A5 0 l0.0 25.0 25.0 25.0 FM) 30.0 25.0 25.0 25.0

Glass in Weight 7! V 0 55.7 46.4 46.4 46.4 A5 0 l(l.l 25.2 25.2 25.2

TABLE l-Contmued Properties T, 260 285 350 295 T, 290 335 400 350 T, 315 360 410 393 T 475 540 570 560 Exp. l/C. 117.9 73.4 93.8 105.4

TABLE 11 Mole 9E V 0, 45 55 75 55 Cs,0 30 30 10 40 1 15.0, 25 15 15 5 sb,o,. HgO

Weight V 0 37.9 46.7 70.2 44.9 Cs,O 39. 39.5 14.5 50.7 M4 0 22.9 13.8 15 3 4.4 Sb-,O HgO Properties T 290 250 280 130 T,- 355 290 300 200 T, 385 360 330 220 T 440 450 480 330 Exp. X/C. 173 174 5 6 7 8 Mole k V 0, 65 45 45 7S Cs- .0 20 30 30 5 As O 15 15 Sh,0;, l0 HgO l0 Weight V,0, 57.9 36.3 37.6 71.8 (15,0 27.6 37.5 38.8 7.4 A5 0 14.5 13.2 13.6 20.8 86 0;, 13.0 HgO 10.0

Properties T, 270 270 320 285 T,- 310 335 380 330 T, 330 350 420 365 T 500 440 530 495 Ex XlO /C,

TABLE I11 Mole "72 V 0 55 55 55 55 55 A5 0,, 15 15 l5 l5 15 PhD 30 15 10 20 Cs,0 30 15 20 10 Weight 71 V 0, 46.7 50.9 48.7 48.0 49.4 A5 0 13.8 15.1 14.4 14.2 14.7 FM) 34.0 16.3 10.7 22.0 Cs,O 39.5 20.6 27.1 13.9

Properties T, 250 320 270 245 290 T; 290 380 340 310 370 T 360 405 390 350 395 T 450 545 510 500 520 Exp. 125- 150C X10 173.8

Glass batches corresponding to these compositions may be prepared by thoroughly mixing together conventional glassmaking ingredients in suitable proportions. Among the various ingredients that may be employed are nitrates, nitrites, oxides, chlorides, and fluorides of lead, cesium, arsenic, vanadium, and the optionals. The selection of batch materials, as well as the selection of melting conditions, depends on the characteristics desired in the glass. Thus, if a glass having low resistivity is desired for semiconducting purposes, conditions favoring a low oxygen content in the glass will be selected. These include selecting AS103 and PbO as batch ingredients and the use of reducing conditions during melting of the glass. In contrast, when a minimum softening point is of paramount importance. oxidizing conditions are selected such as the choice of PbO- and As O as batch ingredients and the use of oxidizing conditions during melting.

A glass batch based on each composition was prepared as described above, placed in a silica crucible and melted at a temperature within the range of 500-900C. for a time within the range of 15-30 minutes. The molten glass was then poured onto a graphite plate and the cast slab placed in an annealing oven.

The coefficient of thermal expansion and the electri cal resistivity were measured on the annealed glass samples. Also, a number of significant thermal measurements were made in accordance with the wellknown Differential Thermal Analysis technique [see, for example, a publication by T. H. Ramsey at pp. 671-5 of the Ceramic bulletin, Vol. 50, No.8 (1971)]. These included the annealing point, the softening point, the melting point, and the crystallization point of the glass. Several of the glass samples were then heat treated to effect thermal devitrification of the glass, that is, controlled crystallization throughout the body of the glass. Thereafter, the coefficient of thermal expansion and electrical resistivity were measured on the devitritied sample. In general, the devitrified glasses showed considerably lower values for both the coefficient of expansion and the resistivity, thus making such thermally devitrified materials useful for conducting purposes.

By way of specific example, test pieces of the first glass in Table l were heat treated at 460C. for 30 min utes to devitrify the glass. The coefficient of thermal expansion was then found to be 88 X 10"'/C. over the range 25l50C. The electrical resistivity was also measured at room temperature and Log R was 1.56 in contrast to 5.92 for the glass before devitritication. Similar tests showed that the coefficient of thermal expansion of glass 3 in Table I dropped to 61.6 X 10 /C. and that of glass 8 to 72.0 X l0/C. after devitrification by heat treatment.

Several additional glass melts were made in the manner described above to compare the effect of various oxides as additives in two typical lead vanadate binary glass batches. The two series of batches, in mole percent, were composed of 1) 47.5% V 0 47.5% PhD, and 5% additive oxide, and (2) 47.5% V 0 47.5% PbO and 5% additive oxide. Glass properties, including softening point, annealing point, crystallization point, and coefficient of thermal expansion were measured as described earlier. The data thus obtained are 5 set forth in Table IV with each of the glasses being identified by the oxide additive to the batch.

TA3LE lV Additive None A 0 As,0, 8,0

Base Glass Properties 1 2 1 2 l 2 l 2 T,(C.) 230 328 300 292 280 275 275 T (C.) 245 365 330 320 295 298 300 Exp. l0 (ZS-150T.) H8 146 138 146 I40 146 Additive SiO B50 Th0, TeO

Base Class Properties 1 2 I 2 l 2 l 2 T (C.) 260 270 265 T -(C.J 270 290 280 Exp): l0 (25l50C) I47 156 The blank spaces indicate that a glass could not be compositions encompassed within the present invenproduced or that the melt crystallized so rapidly on tlOll. Examples 104 were prepared in like manner (0 the cooling that an expansion bar could not be cast. It would appear that B 0 is an effective additive. However, the expansion coefficients of the B 0 glasses are high and, furthermore, their chemical durability is so glass bodies recorded in Tables l-Ill above. Hence, the batch ingredients were placed in an unglazed alumina crucible, melted in an electrically-fired furnace for one-half hour at 700C, the melt poured onto a steel poor as to render them subject to attack by atmoplate, and the resulting slab transferred to an annealer spheric moisture. Such glasses would, obviously, have little. if any, practical utility.

Several further melts were made in the same manner to demonstrate the effect of an optional fourth component in the glasses of the present invention. The base glass was glass 1 of Table I having the following composition in mole percent: 47.5% V 0 47.5% PhD, and 5% A5 0 Each of the recited glass batches was comoperating at 250C. The physical properties tabulated were secured utilizing the Differential Thermal Analysis technique also referred to above.

In preparing Examples 5-20, a method was used which is known to the art as the strip melting technique. This involves placing one or more depressions in a strip of platinum metal, filling the depression(s) with glass batch ingredients (normally about one gram), and then inserting the strip between two electrodes. Elec- Posed of 100 Parts of Such base glass batch with 5 mole tric current is applied between the electrodes and the percent of the indicated fourth component added theretov Table V identifies each glass in the series by the additive fourth component and sets forth the coeffcient of thermal expansion, as well as the various properties measured by DTA measurements.

batch(es) is melted via resistance heating. The resul' tam button(s) is then examined for glass quality. This method permits a rapid survey of compositions to be conducted and is quite useful in predicting the glass stability of larger melts. Examples 5-20 were melted, em-

TABLE V Base SnO, Bi,o sb o TiO Ag AgNO C0 T 265 270 300 290 280 260 240 Ty 328 325 350 350 325 320 280 T 365 365 370 395 360 340 300 T 463 500 510 500 500 510 425 EJtpXlC (ZS-150C.) H8 I3] I 8 9 l0 1 I l2 l3 l4 AgBr H gC I, BaCl 11 0;, TeO SeO Fe o T 280 250 280 245 280 280 320 T, 335 305 335 290 345 350 380 T 355 345 390 340 385 385 4N) T 470 450 480 430 430 480 520 Exp. l0 (ZS-lSlT'CJ I32 Table VI reports a further group of glass composiploying this strip melting technique, for one minute at tions illustrating the glass forming capability of the 9 10 TABLE VI Mole v 0, 55 39.27 74.61 70 47.12 A5 15 10.73 20.39 25 I288 PhO 25 2.5 5 2O 425,0 25 25 2.5 20

Weight v.0. 47.32 32.63 71.93 67.74 40.39 AS203 14.04 9.7 21.38 26.32 12.01 PbO 5.28 25.49 2.96 5.94 21.04 C510 33.36 32.l8 3.73 26.56

Properties T, 280 223 345 315 T, 340 260 395 350 T, 360 285 415 395 TM 435 410 540 450 Exp. 179.3 223.2 74.8 74.9

Mole v.0, 55 55 62.83 70.69 50 415,0 15 17.17 20.31 25 PM) 10 25 10 5 25 05,0 5 10 5 Weight V205 48.0 50.12 7.5 66.96 46.35 785.0; 14.24 14.87 17.09 19.89 25.21 PhD 1071 27.95 11.23 5.81 28.44 C5 0 27.05 7.06 14.18 7.34 11 12 13 14 15 Mole v.0. 55 60 65 55 1 1.68 45,0 25 25 15 32.21 PbO 20 15 10 20 52.34 C520 10 3.77

Weight v,o 51.53 56.82 62.22 48.91 10 A5103 25.48 25.75 26.03 14.51 PbO 22.99 17 43 11.75 22.8 55 Cs,O l3.78 5

Properties TA 280 1,- 310 T,- 320 T 365 16 17 18 19 20 Mole v.0, 28.11 17.29 78.57 87.72 31.42 A5101, 36.18 42.39 9.63 47.43 8.58 PbO 32.07 32.87 8.42 42.04 30 C5 0 3.63 7.44 3.38 3.33 30 Weight v,0 15 15 75 85 25.33 A810; 10 5 7.52 H30 35 35 10 5 29.68 C520 5 l0 5 5 37.47

Devitrified Properties T, 360 315 260 265 T, 390 345 285 285 T.- 395 350 290 290 T 450 400 330 330 Table VI, when viewed in conjunction with Tables 2. A low melting vanadate glass according to claim l [-11], clearly demonstrates the broad glassforming capawherein said composition also contains up to 15% by bilities of the C520 and/or PbO-As O -V O composiweight total of the following metals. expressed in terms tion system. However, Example 20, containing a total of the stated oxide, B2 3. z a, 2 3. 1e02 2, PbO Cs O content of 67.l5 percent by weight. 5 gz 2, 2 :1. 2 a, g 1 and 2- showed instability through the presence of devitrifi- 5 3- A low melting vanadate glass having a compos cation. It will, of course. be appreciated that where 21 tion, in weight percent as calculated on the oxide basis combination of PbO Cs O forms a component of the in terms of PhD, AS203, and V 0 ,cons1st1ng essentially ternary system, both PhD and C5 0 will be present in Of 5 545% 2 3. and 23-35% 2 5 Said amounts greater than incidental impurity levels. glass being essentially free from S10 P 0 A1 0 We claim: L1 0. N320, and K 0.

l. A low melting vanadate glass having a composi- 4. A low melting vanadate glass according to claim 1 tion, in weight percent as calculated on the oxide basis herein Said Composition also contains up to 15 perin terms of C 0, Pb() A 0 and V 0 consisting e cent by weight total of the following metals. expressed sentially of 5-60 percent C520 PbO. wherein both in terms of the stated OXlde. 2 3 2 3 h u 2- Cs O and PbO are present in amounts greater than incidental impurity levels. 5-457: A5 0 and -8577 V 0 said glass being essentially free from SiO P 0 A1 0 Li O. Nil- 0. and K 0.

5e0 Ag O. TiO Fe O 131.0... HgO. B210. and SnO 5. A low melting vanadate glass according to claim 3 wherein said composition consists essentially of 15-60% PbO, 5-3()% As O and 35-607: V 0

12 in terms of the stated oxide. 8,0,. Sb,0;. Tl,0,. TeO,. S803 A810. Tiog. Fcgo Bi,0;, B30. Shogl i i l U 

1. A LOW MELTING VANADATE GLASS HAVING A COMPOSITION, IN WEIGHT PERCENT AS CALCULATED ON THE OXIDE BASIS IN TERMS OF CS2O, PBO, AS2O3, AND V2O5, CONSISTING ESSENTIALLY OF 5-60 PERCENT CS2+PBO, WHEREIN BOTH CS2O AND PBO ARE PRESENT IN AMOUNTS GREATER THAN INCIDENTAL IMPURITY LEVELS, 5-45% AS2O3, AND 25-85% V2O5, SAID GLASS BEING ESSENTIALLY FREE FROM SIO2, P2O5, AL2O3, LI2O, NA2O, AND K2O.
 2. A low melting vanadate glass according to claim 1 wherein said composition also contains up to 15% by weight total of the following metals, expressed in terms of the stated oxide, B2O3, Sb2O3, Tl2O3, TeO2, SeO2, Ag2O, TiO2, Fe2O3, Bi2O3, HgO, BaO, and SnO2.
 3. A low melting vanadate glass having a composition, in weight percent as calculated on the oxide basis in terms of PbO, As2O3, and V2O5, consisting essentially of 5-60% PbO, 5-45% As2O3, and 25-85% V2O5, said glass being essentially free from SiO2, P2O5, Al2O3, Li2O, Na2O, and K2O.
 4. A low melting vanadate glass according to claim 1 wherein said composition also contains up to 15 percent by weight total of the following metals, expressed in terms of the stated oxide, B2O3, Sb2O3, Tl2O3, TeO2, SeO2, Ag2O, TiO2, Fe2O3, Bi2O3, HgO, BaO, and SnO2.
 5. A low melting vanadate glass according to claim 3 wherein said composition consists essentially of 25-60% PbO, 5-30% As2O3, and 35-60% V2O5.
 6. A low melting vanadate glass according to claim 5 wherein said composition also contains up to 15 percent by weight total of the following metals, expressed in terms of the stated oxide, B2O3, Sb2O3, Tl2O3, TeO2, SeO2, Ag2O, TiO2, Fe2O3, Bi2O3, HgO, BaO, SnO2. 